Television system



rniusvisrou' lltudolii Uriel, Germany,

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@riginall application liilay fi l, iiildii 2'i5,t2li.. llllivided and,this appli' to llclle T v u ,iunlren desellschaiit lur tirahtiese Tellin, 1a., h erliri, Geririany, a eorpcration cl Serial No,

lliltl, Serial No. itfiihdhi. lln Genuiany dune ill,

3 iDlaims,

This invention relates to television systems and more particularly tothe method and means for providing interlaced television pictures, andis a divisional of my copending application Serial No. 275,427, filedMay 24, 1939 and entitled Television systems.

In the transmission of television pictures in accordance with the lineskip method, it is known to use an odd number oi lines per picture, sothat the two line sequences are always made up of .a broken number oflines (for instance 122 lines). With this apportioning, oi the number oflines, the lines transmitted during the second line sequence rail in thereceiving image into the interspaces oi the first line sequence. Thenthe frequency or the relatively-slow image for frame frequency (canbedoubled in. the receiving image without requiring a wider transmissionfrequency band than when transmitting by non-interlacing method, andwithout the necessity of carrying out ,adif ferent vertical deviationfor the two line sequences. :l-litherto the opinion has been that thisend could beachieved only when utiliz ing an odd, number oi linesi'oreach complete picture, i. e a fractional number of linesper linesequence.

In accordance with the invention a method is proposed by which thisresult can also be obtaihed with an'even number of lines per image,

1. e. at a whole number of lines per line sequence (at twoline'sequences per picture). To this end, in the second line sequence,the line impulses are so. placed that they have a distance from theimpulses oi the first line sequence which is equal to a number of totalline periods plus one half line period.

Before enumerating the advantages hereby obtainable, the differencebetween the new method and the known method will be described withreference to the drawing in which Fig. l is a graphical sketch of thetime occurrence of line impulses according to the invention and Fig. 3shows in block diagram form apparatus embodying the invention in whichtwo controlled multivibrators of different frequencies are used toalternately key separate channels to provide line synchronizingimpulses.

Fig. 1 relates to the known method, and more specifically to the case ofonly 11 lines per picture chosen for the sake of simplification. Thefirst line sequence covering the time of ,6, second, contains five lineperiods, and the second line sequence likewise extending over secondlikewise contains five line cycles.

The return for therelatively slow picture or (iii. llmiii thl quency.Thus a frame deflection therefore must begin in the center of a linecycle, it the preceding and following return coincide with the beginningof a line cycle, Any line impulse of the second line sequence always hasa distance or time interval irom'the impulse of the first line sequencethat is a whole number measured in line cycles.

Fig. 2 shows the method according to the invention for the simple caseof only 10 lines attwo line sequences per picture. Each of the two linesequences extends over 1 second and covers five total line cycles in themanner indicated by the lines ct toe. The impulse a, has a distance fromthe last impulse of the first line sequence which is'e'qual to one haltline cycle, the impulse t has a distance of 1 line cycles, c has 2 /2line cycles etc. The line impulses of the second line sequence,therefore, have a phase displacement equal to one half of a line cyclerelative to the line impulses of the first line sequence. This can alsobe visualized in such manner that the impulses ci the first linesequence are considered continued within the second line sequence. Theseimpulses would then have the position a to d" shown in dotted lineinliigure 2. The impulses a to c are situated in the center between theimpulses a to d".

At the position a to e of the impulses during the. second line sequence,interlacing is possible in the same way as in the case of an odd. linenumber represented in Figure 1, since in. fact, the impulses a to e fallinto the center of the line when the frame impulse is combined with thedouble picture freline ship transmission can in fact ice-achieved withthe method according to Figure 2.

As compared with known methods, the new one has the advantage that atelevision transmitter can be adapted to'interlaced transmission in asimpler manner when said transmitter was hitherto operated with theordinary picture analyzing. at ordinary picture analyzing the number oflines per picture is always an even number (for instance 180), Thus, incase of 10 lines per picture, the impulses in the first half of thepicture would have the same position as in Figure 2 during the firstline sequence and during the second half of the picture the impulseswould have the position ato (1. There-' fore, it the ordinary pictureanalyzing method is to be converted into an interlaced analyzing method,it is only necessary to delay the impulses a to d by one half line cyclewhereby they assume that position b to c. (it does not matter that thefirst line impulse a will not occur at this displacement, since the.synchronizing impulse for the framing deflection does cover a fewcycles).

The said displacement of the impulses can in fact be carried out in amuch simpler manner in a television transmitter which was operated onlynecessary that during the second half of v picture, a delay device beinserted into the line across which the impulses are passed to thehighfrequency transmitter. It is obvious that in practice this can bedone at less cost than in the case of the replacement of a perforateddisk by one having another division.

If the line impulses are produced by means of a purely electric impulsegenerator, a delay arrangement may likewise be inserted in the impulselin during the second half of the picture. This is likewise a simplermeasure than the providing of a new impulse generator and the'insertionof new frequency divider stages throughout, through which the deflectionfrequency for the frame is derived from the line impulse frequency.

For the insertion of the delay arrangement for the line impulses of thesecond picture half, the synchronizing impulses for the frame deflectioncan be directly used.

As delay means, a multivibrator whose discharge paths have equaloperating periods may be used, and furthermore, also a saw toothgenerator for instance which releases a new impulse when the half of itsamplitude is reached.

In Fig. 3 I have shown in block diagram one arrangement which may beused to provide synchronizing impulses of such order as to produceinterlaced pictures with an even number of integral lines 5| is shown asa source of fundamental frequency control which may, for example,generate the frequency equal to the line frequency. Two multivibrators53 and 55 are provided and are fed with the control frequency, themultivibrator 53 being a frequency divider so as to provide an outputhaving a frequency equal to the frame frequency, while the multivibrator55 is used as a frequency multiplier and has its constants so chosen asto provide a frequency equal to twice the frequency of the lineimpulses. Alternatively, 5| may actually feed impulses having afrequency equal to the frame frequency to the multivibrator 53 as wellas feeding impulses equal to twice the line frequency tothemultivibrator 55. The use of the multivibrators is to provide asubstantially rectangular wave form, and as is well known, by takingoutput energy, for example, from the two plate circuits of themultivibrator there will be derived energy which has identical waveshape, except that one wave will be 180 degrees out of phase with theother, as is well known and as is shown, for example, on page 273, Fig.131, of the textbook Radio Engineering" by Terman, McGraw Hill Book Co.,New York, 1932. The same procedure is used with respect to themultivibrator 55- and accordingly, there will be derived from themultivibrator 53 the frame frequency impulses 54 and 54', while from themultivibrator 55 there will be obtained the wave forms 55 and 56' equalto twice the line frequency. The use of multivibrators for frequencymultiplication and dividing, is, of course, well known and is shown forexample, in U. S. Patent No. 2,132,655 to J. P. Smith, entitled Systemfor producing electrical impulses" which issued October 11, 1938.

The outputs from th multivibrators 53 are fed respectively to the twokeying stages 5'! and 59, while the two outputs from 55 are fedrespectively to the same keying stages. Thus each of the keying stages51 and 59 are controlled by the combined impulses of 54 and 58 and 54and 56' so that alternatively, one or'the other of the two stages iskeyed and thus can provide an output. The outputs of the two keyingstages are then fed to their respective wave shaping circuits BI and 63and the outputs combined and fed, for example, to the radio transmitterof the television system. The wave shaping may be done, as shown in theabove identified Smith Patent No. 2,132,655, or may be accomplished bythe us of impedance correcting networks, such as shown in Smith PatentNo. 2,045,315, issued June 23, 1936, for "Television system or StockerPatent No. 2,045,316, issued June 23., 1936, for Impedance coupledamplifier. The keying of the impulses may likewise be accomplished afterthe fashion shown in the first mentioned Smith patent. Under theseconditions, the two keying stages will provide the line frequency forthe two line sequences wherein the phase shift for the second of the twosequences is provided with a delay equal to one half the time periodnecessary to scan one line. The wave shaping circuits are merelyprovided to either elongate or shorten the pulses before being mixedwith the picture signals for transmission by the radio transmitter.

a line cycle.

Having described my invention, what I claim is:

1. A synchronizing system for an even line interlaced television systemcomprising means for supplying frame synchronizing and double linesynchronizing frequency impulses, a multivibrator fed by the framesynchronizing impulses, a multivibrator fed by double line frequencyimpulses, means to derive output energies having out-of-phase componentsfrom each of the multivibrators, two keying stages each fed with energyderived from each of the two multivibrators, means to shape the outputof each of the keying stages, and means for combining the outputs of thekeying stages.

2. A synchronizing system for an even line interlaced television systemcomprising a first multivibrator, a secondmultivibrator, common meansfor controlling both of said multivibrators, means to derive outputenergies having out-ofphase components from each of the twomultivibrators, means to combine a portion of the derived energies ofeach of the multivibrators, means to combine other portions of thederived energies of the two multivibrators, means to shape each of thecombined energies, and means to combine both of the shaped energies.

E. A synchronizing system for an even line interlaced television systemcomprising a source of control frequency, two separate relaxation Ioscillators, means to control each of the relaxation oscillators bydifferent energy from the source of control frequency, means to derivefrom each of the relaxation oscillators energy having ing the shapedenergies the same wave shape but displaced in phase from each other,means to combine the energies from the two relaxation oscillators whichhav minimum phase angle, means to combine the energies from therelaxation oscillators having maximum phase angle, independent means toshape each of the combined energies, and means for combin-

